A wide range of different types of light-emitting diodes (LEDs) exist on the market and are available “off-the-shelf”. Each type of LED has a set of operating conditions defined, for example, by the minimum and maximum values of voltage and current for which the LED will operate correctly. Each type of LED also has a set of intrinsic performance characteristics, for example, an achievable light intensity of light produced by the LED. This is relevant when used in the context of optical light communication. Other intrinsic performance characteristics of LEDs are also relevant in such a context. For example, LEDs have an intrinsic modulation frequency bandwidth dependent on the method of manufacture and the materials the LED is made of. For example, Organic Light Emitting Diodes (OLEDs) typically have a low modulation frequency bandwidth in the region of hundreds of kilohertz. However, solid-state LEDs typically have higher modulation bandwidth in the region of several megahertz.
Luminaires for optical light communication are designed to serve a specific purpose. The design of a driver circuit of the luminaire may be tailored to incorporate a specific type and/or number of LEDs. In particular, the driving circuit may be tailored to the operating conditions of the LED to provide good performance. The driving circuit can also be tailored to one or more LEDs to provide improved performance compared to the individual intrinsic performance characteristics of the individual LED.
In general, a bespoke driving circuit tailored to a specific type of LED may not be suitable for use with a different type of LED. Reasons for unsuitability include the bespoke driving circuit being set to provide a voltage and/or current that is insufficient for the chosen type of LED, in effect leading to a reduced quality optical signal. The performance of other components in the driving circuit are also dependent on the type of LED connected to the driving circuit and using an LED type other than the type for which the driving circuit was tailored can lead to inefficiency in the operation of the LED and the other component parts. For example, if a component of a driving circuit is a transistor, the use of an LED that requires different voltage levels to operate in the same current signal range may cause the transistor to dissipate unnecessarily high thermal energy levels leading to inefficiency in the driving circuit. Transistors are also built with a finite tolerance to voltage drop before the transistor is destroyed. Therefore, connecting a different type of LED carries the risk of destroying the transistor.
As is known, visible light communication uses intensity modulation of LEDs. An intrinsic property of LEDs is their response to an input current, which varies from LED to LED and can be characterised using a frequency modulation bandwidth. A different type of LED connected to a tailored LED driver may not be able to provide a sufficient quality of signal, as measured by a signal to noise ratio, over the full modulation bandwidth originally intended.